Eighty-four speed of sound values in gaseous mixtures of the refrigerants difluoroethane (CH3CHF2, HFC152a) + difluoromethane (CHCIF2, HCFC22) have been measured for temperatures from 293 to 323 K, pressure from 200 to 405 kPa, and mass fractions of HCFC22 of 13.8 and 25.5% with a spherical acoustic resonator. The experimental uncertainties in the temperature, pressure and speed of sound in gas are estimated to be less than +/-14 mK, +/-2.0 kPa and 0.0037%, respectively. The compositions of the binary mixtures HFC152a + HCFC22 have been accurately determined and 14 acoustic virial coefficients have been obtained from the present speed of sound measurements. The purities of HFC152a and HCFC22 are better than 99.95 mass%.